1. Field of the Invention
The invention relates to a short arc discharge lamp and a light source device using this lamp. The invention relates especially to an improvement of the starting properties of this short arc discharge lamp.
2. Description of the Related Art
In a short arc discharge lamp, in general, as shown in the schematic in FIG. 1, a trigger wire 5 is mounted on the outside of an arc tube 10, bridging two hermetically sealed portions, and is wound around the hermetically sealed portions 6. This trigger wire 5 has the function of lowering the breakdown voltage when the lamp starts. In FIG. 1, H.V. designates a high voltage pulse generator. The short arc discharge lamp is used for a DLP® projector (as made by Texas instruments), which is a high pressure rare gas discharge lamp. Since, in a high pressure rare gas discharge lamp, the filling pressure of the rare gas is high and the possibility is great that the lamp will easily break, it is undesirable to bring a foreign body into contact with the outside of the arc tube 10. However, since the increase of the filling gas pressure results in an increased breakdown voltage, a trigger arrangement is essential to facilitate the proper starting of the lamp. Consequently, the trigger wire 5 is mounted as was described above.
In the above described FIG. 1, there are the following disadvantages.                In situations in which the arc tube is scratched, i.e., in the course of operation in the area on the outside of the arc tube 10 that has made contact with the trigger wire 5, crystallization takes place and in this way devitrification occurs.        In the area in which the trigger wire 5 has been laid along the outside of the arc tube 10, the radiant light which is emitted by the arc tube 10 is shielded.        During operation, the arc tube 10 reaches a high temperature and the trigger wire 5 becomes oxidized and degraded. Therefore, the starting ability is degraded with increased frequency of operation.        When the trigger wire is positioned on the outside of the arc tube, high voltage breakdowns occur, which are dangerous when a short arc discharge lamp is combined with a concave reflector, i.e., when a light source device is formed in which the mirror surface is in close proximity to the arc tube. Therefore, it is difficult to increase the size of the focusing area.        